Which version do I choose?

IIS

If you are using PHP as FastCGI with IIS you should use the Non-Thread Safe (NTS) versions of PHP.

Apache

Please use the Apache builds provided by Apache Lounge.
They provide VC9, VC11 and VC14 builds of Apache for x86 and x64.
We use their binaries to build the Apache SAPIs.

If you are using PHP as module with Apache builds from apache.org (not recommended) you need to use the older VC6 versions of PHP
compiled with the legacy Visual Studio 6 compiler. Do NOT use VC9+ versions of PHP with the apache.org binaries.

With Apache you have to use the Thread Safe (TS) versions of PHP.

VC9, VC11 & VC14

More recent versions of PHP are built with VC9, VC11 or VC14 (Visual Studio 2008, 2012 or 2015 compiler respectively) and
include improvements in performance and stability.

- The VC9 builds require you to have the Visual C++ Redistributable for Visual Studio 2008 SP1x86 or x64 installed

- The VC11 builds require to have the Visual C++ Redistributable for Visual Studio 2012x86 or x64 installed

- The VC14 builds require to have the Visual C++ Redistributable for Visual Studio 2015x86 or x64 installed

TS and NTS

TS refers to multithread capable builds. NTS refers to single thread only builds. Use case for TS binaries involves interaction with
a multithreaded SAPI and PHP loaded as a module into a web server. For NTS binaries the widespread use case is interaction with a web server through
the FastCGI protocol, utilizing no multithreading (but also for example CLI).

What is PGO?

Profile Guided Optimization is an optimization
feature available in Microsoft's Visual C++ compiler that allows you to optimize an output file based on profiling data collected during test runs of the application or module.